1. Field of the Invention
This invention relates to virtual volumes and more particularly relates to presenting virtual attributes to a host.
2. Description of the Related Art
Data processing systems such a computer workstations, servers, mainframe computers, and the like typically store data on one or more storage devices. In one embodiment, a storage controller manages the storage devices. For example, the storage controller may initialize the storage devices, perform maintenance operations on the storage devices, and write data to and read data from the storage devices. In a certain embodiment, a storage server may manage communications between a data processing system and a storage controller. The storage server, storage controllers, and storage devices may be embodied in a storage subsystem.
A storage device may be a hard disk drive, an optical storage drive, a magnetic tape drive, or the like. The storage device may be organized as one or more physical volumes. Each physical volume may have a number of distinguishing physical attributes such as data storage capacity, a number of cylinders, a number of tracks on a cylinder, a number of sectors on a track, a data capacity of a track, a data capacity of a data block, and the like.
The storage device often stores large amounts of valuable data. To protect against loss of the data, an administrator of the data processing system will typically direct a software process to back up the storage device by copying data from the storage device to another storage device. In one embodiment, the software process may make a snapshot copy. The snapshot copy or point-in-time copy is a copy of a specified instance of the data, such as the instance of the data at a specified time.
The software process that creates the snapshot copy typically writes metadata and data from a primary physical volume to a target physical volume. The primary physical volume and target physical volumes are referred to herein as the primary volume and the target volume respectively. The metadata may describe the data, including the source of the data and the time the snapshot was created. In one embodiment, the metadata is written to the beginning addresses of the target volume. The software process may write the data after the metadata to subsequent target volume addresses. Alternatively, the software process writes metadata to the target volume at addresses subsequent to the addresses of the data.
In addition, the software process may write data from the primary volume to the target volume when the primary volume is idle to minimize the impact of the backup operation on primary volume performance. The software process may also delay copying a data block from the primary volume to the target volume until just before the data block on the primary volume is overwritten.
Thus the backup software process may be configured to write data blocks from the primary volume to predetermined addresses in the target volume. As a result, the backup software process is often designed to only backup data to a target volume with substantially similar physical attributes to the primary volume to assure that there is sufficient space for all data blocks and metadata when copied to the target volume.
Unfortunately, limiting target volumes to the physical attributes of the primary volume constrains the flexibility of the data processing system administrator in configuring the storage subsystem. For example, the administrator may include only physical volumes of a specified capacity in the storage subsystem to assure that sufficient target volumes are available to backup each primary volume. This may prevent the administrator from adding larger capacity, more cost efficient storage devices over time.
From the foregoing discussion, it should be apparent that a need exists for an apparatus, system, and method that present a virtual physical volume attribute. Beneficially, such an apparatus, system, and method would allow a storage subsystem to employ storage devices with a plurality of physical attributes.